I use the 18 qt electric roasters for cheese making. I don't put water in the outer heating part, under the pan. I have a Nesco roaster and then a Bella roaster from a rummage sale, $10. I've made about 92 batches of 4 gallons each, 33 kinds of cheese.
A thermometer tells me the temperature, the dial on the roaster for temperature tells me if it is heating or if I want, I turn it off. There is some residual heat in the roaster so it gets turned off before reaching target temperature. After a while, I just got used to it.
Many of the electric roasters have non-stick finishes on the pan. This will be a problem over time, so I scrubbed the non-stick finish off and it works well.